The present disclosure relates to vehicular radio communications systems for establishing a bi-directional digital radio communications link between a local wireless communication device inside a moving vehicle and a sequence of radio transceivers in a wireless network external of said vehicle.
Cars currently can have multiple external antennas for various different purposes, for example: receiving and sending LTE (long term evolution) cellular transmission as in the 4G mobile communications standard; receiving digital audio broadcasts (DAB) or other digital audio broadcast, such as HD Radio (Reg. TM); and receiving and sending data in a wide area network (WLAN), for example by using WiFi (Reg. TM).
It is known to use multiple external antennas, and two is usual, when receiving so that frequencies can be switched when coming into range of a better signal. An additional “sniffing” antenna can be used to monitor signal strength across a range of frequencies.
Cars can have multiple internal antennas for retransmitting the signals inside the vehicle. Clearly, the same frequencies cannot be used simultaneously both inside and outside the vehicle or else there will be interference. Different frequencies are therefore used internal to the vehicle.
Some types of electronic component used with in-vehicle communications system are relatively expensive. The simplest, but most expensive, way of providing receive/transmit paths both inside and outside the vehicle is to use many separate receive RF paths and many separate RF transmit paths, both for inside and outside the vehicle. The conventional approach is for each antenna to have its own, separate RF circuitry covering all the bands and frequencies for that antenna. However, when the RF paths are all separate, there can be the need for many of the relatively expensive RF power amplifiers, not to mention duplication of less expensive components.
It would be desirable to have a solution which is “worldwide” so that the same “box” can be supplied to an auto manufacturer regardless of where in the world the vehicle will be sold. LTE 4G mobile is a particular problem as there are currently 45 bands globally. Each band covers a spread of frequencies. There is one cluster of LTE bands between 700 MHz and 950 MHz, and another cluster about 1.4 GHZ and about 2.7 GHZ and a few at between about 3.4 GHz and 3.8 GHz. When there is a single antenna, 90 RF paths (receive and transmit) would be needed external to the vehicle and 90 RF paths internal to the vehicle in order to provide functionality across all 45 bands. In practice, different regions of the world have different combinations of bands, so not all paths would need to be implemented if a vehicle is to be used in just one of these regions. However, as there is a desire to standardise vehicular components worldwide, as far as possible, in principle this would require all equipment implementing all 90 paths, both externally and internally to the vehicle.
With two antennas both external and internal, these numbers double. To this can be added the requirement to provide for WiFi communication with additional antennas and circuitry. There are currently two WiFi bands, but this will probably expand to 5 to 7 in a few years.